The present invention relates to a reticle and, more particularly, to a reticle and a method of manufacturing the same. Micro patterns in the reticle can be formed by improving the resolutions of exposure equipment by employing a difference in the refractive index between media.
In the manufacture of semiconductor devices, photolithograph technology is used to form patterns on a semiconductor substrate. In this photolithographic process, a photomask pattern is transferred as a photosensitive resin phase deposited on the semiconductor substrate by means of a reduction projection exposure apparatus, so that a desired pattern of the photosensitive resin is developed and obtained.
The photomask is a negative plate for projection exposure. The photomask is formed by depositing a light-shielding layer on a transparent substrate, and then by partially removing the light-shielding layer to form a transmission region and a light-shielding region. That is, the reduction ratio of the projection exposure apparatus (the size of a pattern on the photomask versus the size of a formed image) is not 1:1. The negative plate of reduction projection exposure is particularly referred to as a “reticle”.
FIG. 1 is a cross-sectional view of a conventional reticle.
Referring to FIG. 1, the conventional reticle 100 includes chrome (Cr) layer patterns 120 patterned at regular intervals below a quartz substrate 110, a frame 130, a pellicle 140 for preventing the attachment of alien substance in a photolithograph process, and an air layer 150 between the quartz substrate 110 and the pellicle 140.
The Cr layer patterns 120 are made of Cr capable of completely shielding light. A portion in which the Cr layer patterns 120 are formed becomes a light-shielding region A. A portion including only the quartz substrate 110 between the Cr layer patterns 120 becomes a transmission region B through which light can pass. The air layer 150 is formed between the transmission region B and the pellicle 140, and causes air to serve as a medium.
FIG. 2 is a view illustrating the traveling path of light passing through the conventional reticle and a numerical aperture (NA).
The path of light passing through a reticle 200 having a half-pitch (p) is described below with reference to FIG. 2.
Light 260 incident on a quartz substrate 210 at an incident angle θi is refracted from a boundary surface between a quartz substrate 210 having a refractive index of 1.5 and an air layer 250 having a refractive index of 1 within the transmission region B at an angle of θr. At this time, the light 260 moves from the quartz substrate 210 having a high refractive index to the air layer 250 having a low refractive index. Thus, the refracted angle θr becomes greater than the incident angle θi according to Snell's law.
Thereafter, the refracted light 260 passes through a pellicle 240 and is then focused on a lens 270. The lens 270 is disposed under the reticle 200 and has an NA of a specified amount.
In recent years, semiconductor products have become miniaturized and highly integrated. Thus, processes and methods for increasing the resolution limit (hereinafter, referred to as the “resolution”) in an exposure process are required. Of them, there has been proposed a method of reducing the half-pitch of the reticle by decreasing the size of the Cr layer patterns in the reticle itself.
FIG. 3 is a view illustrating the path of light passing through another conventional reticle and the NA.
The path of light passing through a reticle 300 having a small half-pitch p1 as Cr layer patterns 320 become small is described below with reference to FIG. 3.
Light 360 incident on a quartz substrate 310 at an incident angle (not shown) is refracted from a boundary surface between a quartz substrate 310 having a refractive index of 1.5 and an air layer 350 having a refractive index of 1 within the transmission region B at an angle of θm.
At this time, the light 360 moves from the quartz substrate 310 having a high refractive index to the air layer 350 having a low refractive index. Thus, the refracted angle θm becomes greater than the incident angle according to Snell's law.
Thereafter, the refracted light 360 passes through a pellicle 340 and is then focused on a lens 370 disposed under the reticle 300 and having an NA of a specified amount. However, some of the refracted light 360 is not focused on the lens 370 and it is therefore radiated to the outside. Reference numerals 230 and 330 indicate frames, and A indicates the light-shielding region in which light is shielded.
If the chrome layer patterns 320 of the reticle 300 become small and the half-pitch p1 becomes small in order to form a micro pattern as in the prior art, a difference in the path of the light 360 passing between the Cr layer patterns 320 in the structure of the reticle 300 in which the air layer 350 is used as a medium results in greater refraction according to the following Equation 1.
                                          sin            ⁢                                                  ⁢            θ                    =                      λ            p                          ,                            (        1        )            where θ is the refracted angle, λ is the wavelength of a light source, and p is the half-pitch of the reticle.
Therefore, in the case where the same NA is used, if the half-pitch of the reticle becomes small as shown in FIG. 3, the refracted angle increases. Accordingly, because the +1 order light required for patterning is not focused on the lens, there is a problem in that micro patterns are not implemented on a wafer.
Due to this, it is necessary to develop and purchase new and expensive exposure equipment to form micro patterns exceeding the resolution of existing exposure equipment.